In the preface to his The Great Divorce, C.S. Lewis wrote the following:
“The attempt [of William Blake’s The Marriage of Heaven and Hell] is based on the belief that reality never presents us with an absolutely unavoidable ‘either-or’; that, granted skill and patience and (above all) time enough, some way of embracing both alternatives can always be found; that mere development or adjustment or refinement will somehow turn evil into good without our being called on for a final and total rejection of anything we should like to retain. This belief I take to be a disastrous error. You cannot take all luggage with you on all journeys; on one journey even your right hand and your right eye may be among the things you have to leave behind. We are not living in a world where all roads are radii of a circle and where all, if followed long enough, will therefore draw gradually nearer and finally meet at the centre; rather in a world where every road, after a few miles, forks into two, and each of those into two again, and at each fork you must make a decision. Even on the biological level life is not like a pool but like a tree. It does not move towards unity but away from it and the creatures grow further apart as they increase in perfection. Good, as it ripens, becomes continually more different not only from evil but from other good.
“I do not think that all who choose wrong roads perish; but their rescue consists in being put back on the right road. A wrong sum can be put right: but only by going back till you find the error and working it afresh from that point, never by simply going on. Evil can be undone, but it cannot ‘develop’ into good. Time does not heal it. The spell must be unwound, bit by bit, ‘with backward mutters of dissevering power’ – or else not. It is still ‘either or.’”